[Proposal] Add instance Monoid a => Monoid (Const a b)

Edward Kmett ekmett at gmail.com
Sat Oct 12 18:30:56 UTC 2013

That is a pretty solid argument for moving Compose.

Especially as Traversable will be transitioning into the Prelude in 7.10.


On Sat, Oct 12, 2013 at 1:57 PM, Gershom Bazerman <gershomb at gmail.com>wrote:

> On 10/12/13 1:32 PM, Edward Kmett wrote:
>> Between moving Identity into base and removing Constant it would mean
>> that transformers would then only have to contain ...well.. transformers. =)
>> -Edward
>>  Well, not quite. Compose should migrate into base at well at some point,
> I think. Especially since currently we have traversable laws in base using
> a datatype _not_ in base!
> I can see an argument in favor of Product as well, but also an argument,
> perhaps, that the product of two functors is somewhat less common than
> their composition.
> I consider the whole "polynomial functor toolkit" as pretty basic. But I
> can see a slippery-slope danger that we should only bring in those
> components that make other "basic" parts of base more elegant.
> Also, we should bear in mind that "growing" the algebraic part of base
> (Traversable, Functors, etc.) doesn't necessarily go against the spirit of
> then taking these slightly larger units of conceptual functionality and
> splitting them out from "core-base" in the next go-round.
> --Gershom
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